【作者】 邹明松；

【导师】 吴有生； 司马灿；

【作者基本信息】 中国舰船研究院 ， 船舶与海洋结构物设计制造， 2014， 博士

【摘要】 多年来，国内外对船舶结构流固耦合振动和声辐射特性问题开展了许多理论和试验研究。许多研究针对大为简化的平板、加筋平板、加筋圆柱壳等典型结构形式，在无界均匀介质中的振动与声辐射；试验研究亦多为缩尺度模型机理试验。尽管该领域的研究取得了很大的进展，如何科学地反映流体与水中结构在振动与声辐射过程中的耦合作用，分析阐明一艘船舶在不同水深、不同潜深、不同方位和距离上形成辐射声场的分布特征和相互之间的差异，说明振动、船体近旁自噪声和远场辐射噪声之间的传递和演变规律，成为船舶振动噪声领域关注的一个问题。这要求进一步发展一个适于任意形状的、具有复杂内外结构的船舶，能计及自由液面、海底及航速影响，具有可接受的工程计算精度，计算量能为现有船舶研究与设计部门的计算机系统能力承受的船舶三维声弹性计算分析理论和方法。本文正是针对该工程背景，在Wu（1984）建立的浮体三维水弹性力学理论的基础上，有所创新和拓展，发展建立了船舶三维声弹性理论及计算方法。具体包含六部分内容。第一部分，通过引入计及自由液面效应的理想可压流体Green函数，并基于Price-Wu广义流固界面条件，建立了带航速和考虑自由液面的均匀声介质中的船舶三维声弹性理论。该理论既适用于声辐射问题，也适用于声散射问题。由于在船舶声弹性理论中计入了航速的影响，理论上更加完备。量阶分析和数值计算表明，航速对船舶流固耦合振动及水下声辐射会有影响，但其影响主要限于低频域及近场区。第二部分，针对我国近海的实际情况，重点考虑浅海海底与水面的影响，暂不计及海水密度与声速等的变化与分层，将均匀声介质中的船舶三维声弹性理论与海洋声传播理论相结合，引入Pekeris水声波导模型，建立了有限水深海洋声学环境中的船舶三维声弹性理论及分析方法。详细论述了耦合求解三维结构声弹性响应的动力学方程和水声传播方程的方法与步骤，并针对常见浅海的特征，给出了Pekeris波导Green函数的近似级数表达式，有效降低了数值计算的复杂度、减少了计算量。第三部分，为提高上述船舶三维声弹性理论及分析方法的工程实用性，建立了三种配套的有助于增加计算效率和解决常用工程问题的专用计算方法：其一，船舶声弹性子结构分离与集成方法（SSSI方法）和解析/数值混合子结构方法（MANS方法）。建立了能有效提高计算效率，特别适用于解决船体内部子结构（如横舱壁、铺板、基座等）振动噪声传递效果分析及优化的船舶声弹性子结构分离与集成方法。其主要思想是：将主船体与船内子结构分离，采用模态综合超单元方法形成子结构的输入输出自由度缩聚动刚度矩阵，采用三维声弹性方法实现主船体与水介质的流固耦合求解，通过边界连接条件完成主船体与子结构的综合集成。进而针对潜艇类水下船舶主体结构的特征，采用两端简支单层加肋圆柱壳解析计算模型来描述主船体结构，应用解析方法求解流固耦合作用，建立了解析/数值混合的声弹性子结构方法。该方法可有效提高计算效率和扩展计算频段范围。其二，敷设声学覆盖层的船舶三维声弹性分析方法。针对船舶表面敷设声学覆盖层降低声目标强度和水下辐射噪声这一工程问题，进一步建立了敷设声学覆盖层的船舶三维声弹性力学理论和计算方法。通过引入描述声学覆盖层内外表面间声振传递的四端参数法，实现“船体结构‐声学覆盖层‐水介质”的声振耦合求解。其三，双流域耦合的三维声弹性分析方法。针对双层壳水下船舶存在舷间水耦合的特点，进一步发展了双流域耦合的船舶三维声弹性计算方法，扩展了工程应用的范围。第四部分，针对简单源汇分布法（简称简单源方法）中不规则频率问题，提出了虚拟阻抗封闭曲面法（CVIS方法）。以往在声弹性领域的边界元计算中较多地采用Helmholtz积分方法，先后曾发展了多种应用Helmholtz积分方法时处理不规则频率处解的非唯一性问题的方法。采用简单源汇分布法求解声场时同样存在不规则频率问题。本文根据简单源汇分布法中不规则频率产生的机理，提出了在浮体内部的虚拟流场中引入一个虚拟的阻抗封闭曲面，用于吸收声振能量，抑制内部虚拟流场的共振，有效地消除了声学问题求解时易出现的不规则频率。汇聚上述内容，形成了一套较完整的可用于分析复杂船舶结构低中频段振动与声辐射的声弹性理论框架、数值方法和应用工具。在此基础上，编制了数值计算程序，作为一个单独的模块（声学计算模块）并入到大型水弹性计算软件THAFTS中。第五部分，本文采用算例与解析解的比对和试验验证的手段，对理论、计算方法和计算程序模块的正确性、实用性进行了考核验证。其中的试验验证包括开阔有限水深环境中小尺度舱段结构的声辐射试验验证和水池内实尺度船体舱段结构振动响应及水中声辐射的试验验证。比对和验证的结果表明，本文所述的理论方法和计算程序能有效应用于复杂船舶结构的声弹性响应分析预报。第六部分，围绕在船舶辐射噪声工程领域人们密切关注的问题，利用本文建立的理论、计算方法和软件开展了选取不同采样时段声压信号对船舶声源级评定的影响、不同距离处的声压值对船舶声源级评定的影响、不同水深和潜深环境对船舶辐射噪声的影响以及不同方位的声压特征对船舶声源级评定的影响四方面的应用研究。据于该研究的数例，建议了可操作性较强、能稳定地反映船舶辐射噪声频谱特征及噪声级评定结果的采样和声压信号处理方法；给出了不同水深和潜深环境中船舶近远场辐射声的分布特征、可供参考的初步规律；提出了利用本文的方法和程序计算一艘船在不同水深和潜深环境中的辐射噪声频谱，进而归纳出该船在给定频段内的总声级在不同水深与潜深中换算关系的修正图谱的建议，并给出了两幅可用于把示例船在浅水或小潜深状态下的噪声级采样评定结果修正到其它水深潜深的图谱的例子。最后，给出了应用本文开发的计算软件预报多种机械设备激励引起的实船结构振动和水下辐射噪声的简要示例，与测试结果作了比对，说明了方法与软件的可用性。目前，该计算方法与软件已在多个工程项目中应用。更多还原

【Abstract】 For many years, theoretical and experimental researches on the fluid-structure coupledvibrations and sound radiations of a ship have been carried out at home and abroad. A varietyof published research works in this field were about the vibrations and sound radiations oftypical simplified structures such as a flat plate, a stiffened plate and a stiffened cylindricalshell etc. in unbounded uniform fluid field. The corresponding experimental studies weremostly conducted for the mechanism investigations based on the tests of small scale models.Although great progress has been made in the past decades in this research field, it still hasbeen a focusing point about how to rationally represent the coupled fluid-structureinteractions in describing the distribution characteristics and clarifying the differences ofmachinery excited radiation sound fields of a ship in different water depth, differentsubmerging depth, different observation distance and direction, as well as in identifying thetransmission and variation behaviors of near field self-noise and far field radiation noise. Thisrequires the further development of a three-dimensional sono-elastic analysis method that isexpected to be suitable for ships with arbitrary shapes and complicated internal and externalstructures, capable to include the influence of free surface and sea bed, the effect of forwardspeed of the ship in the vibration and noise predictions, and also having acceptable numericalaccuracy and adequate computational demand in engineering applications to a full scale ship.It is against to this engineering background, as a creative extension and furtherdevelopment of the existing three-dimensional hydroelasticity theory of Wu (1984), athree-dimensional sono-elasticity theory of floating bodies is presented together with thecorresponding numerical methods in this thesis. The major achievements contained in thisthesis are as follows.1. The first, a three-dimensional sono-elasticity theory of a ship advancing in uniformacoustic medium with free surface is established by introducing the Green’s function for theideal compressible fluid and employing the Price-Wu generalized fluid-structure interfaceboundary conditions. This theory is applicable to either the sound radiation problem or thescattering problem. As the result of inclusion of the forward speed effect of the ship, thesono-elastic theory of ships seems theoretically more complete. The order analysis of theformulas and the numerical examples show that the ship speed will influence the coupledvibration and sound radiation. However the influence is only limited to the low frequencyrange and near field. 2. The second, in view of the actual geographical conditions of shallow China Sea,paying attention to the effects of sea bed and free surface, rather than the influence of waterdensity and sound velocity variations and stratum in depth, a three-dimensionalsono-elasticity theory of a ship in ocean acoustic environment of finite depth and thenumerical methods are established. To achieve this, the three-dimensional sono-elasticitytheory of a ship in uniform acoustic medium is combined with the ocean sound propagationtheory and the Pekeris waveguide model. The methods for solving the coupled dynamicequations of sono-elastic responses of the structure and the waveguide equation for acousticpropagation are presented in detail. An approximate series expansion formula of the Pekeriswaveguide Green’s function is described to greatly reduce the complexity in acoustic fieldcomputations.3. The third, three specific techniques are proposed for increasing the computationalefficiency and fulfilling the requirements of practical applications of the three-dimensionalsono-elasticity theories of ships and the corresponding numerical methods:(1) A ship sono-elastic sub-structure separation and integration method (SSSI) and amixed analytical-numerical sub-structure method (MANS)By separating the ship outer hull and the internal sub-structures (such as the bulkheads,decks, machinery foundations etc.), employing the super-element modal synthesis method toform the dynamic stiffness matrices of condensed input and output degrees of freedom,solving the coupled fluid and outer-hull interaction equations, and finally integrating the mainouter-hull and the internal sub-structures with their conjunction boundary conditions, the SSSImethod is proposed. This method has an intrinsic ability to enhance the calculation efficiencyand is particularly applicable to predict and to optimize the vibration and noise propagationamong ship hull and sub-structures. Further more, for a submerged vessel, a submarine or anAUV for example, the outer main hull can be modeled as a single-hull stiffened cylindricalshell simply supported at both ends, its fluid-structure interaction problem can be analyticallysolved, while the sub-structure inside the vessel can be numerically modeled. The MANSmethod may then be established to predict the sono-elastic responses of the vessel. Thismethod increases the computational efficiency as well as the frequency band of the responsesolution.(2) The sono-elastic analysis method for a structure covered with acoustic layersAcoustic layers, anechoic tiles so to call, are commonly used to cover on the hull surfaceof a submarine for depressing the deflected acoustic signal and the self radiated noise. Toallow for prediction of the sono-elastic responses of a underwater structure covered with acoustic layer, the three-dimensional sono-elasticity theory and numerical method are furtherextended by introducing a four-terminal parameter method to describe the acoustic wavetransmission behavior between the inside and outside surfaces of the acoustic layer. Thecoupled sono-elastic responses of the “hull structure-acoustic layer-water medium” systemmay then be solved.(3) The sono-elastic analysis method for a coupled fluid-structure system withdouble-fluid regionsIn a double-hull underwater vessel, water is filled in broadside space between the outerand inner hulls. The three-dimensional sono-elasicity theory is further modified toaccommodate the coupled response analysis of the system with double-fluid regions.4. The fourth, a “Closed Virtual Impedance Surface (CVIS) Method” for depressing the“irregular frequencies” encountered in the numerical solutions based on the sourcedistribution method is proposed. In the past decades the Helmholze integral method werewidely employed in solving the sono-elastic problems. Certain methods were simultaneouslydeveloped to successfully eliminate the problem of non-unique solutions appeared as the“irregular frequencies”. When applying the simple source distribution method instead of theHelmholze method, the problem of irregular frequencies also exists that remains as a difficulttask to deal with. In this thesis it is proposed to introduce a virtual closed surface withprescribed impedance inside the imaginary fluid region occupied by the floating body (theship). This surface absorbs the acoustic energy and suppresses the cavity resonances in theimaginary fluid region, and hence efficiently eliminates the irregular frequencies.The above results have formed a set of theoretical framework, numerical methods andapplication tools for sono-elastic analysis of the coupled vibration and acoustic radiation of acomplicated ship structure in the low and medium frequency range. The computer programdeveloped in this work has been integrated into the software entitled “Three-dimensionalHydroelastic Analysis of Floating Traveling Structures”(THAFTS) as an individual“Acoustic Module”.5. The fifth, for vilification and validation purposes, a number of numerical examples areused to compare the predictions obtained by the present methods and programs with theavailable analytical solutions of typical simple structure, the published data, and theexperimental results. The experimental data used in the comparisons include the structuralvibrations and acoustic pressures measured in the tests of a small scale stiffened cylindricalhull in open water with finite depth, and a two-cabin segment of an full scale old ship in alarge water basin, both were excited by operating machineries. The comparisons show that the present theory, numerical method and the corresponding program can be efficiently applied topredict the sono-elastic responses of a ship.6. The sixth, as a part of application examples, the method and program presented in thisthesis are particularly used to investigate and examine the following problem that is of greatinterests in measuring and assessing the noise source level of a submerged ship: thequantitative influences of the sampling duration, the observation distance and direction of thepressure measurement, the water depth and submerging depth of the ship on the assessment ofthe ship’s radiation noise source level. Based on the investigations, the reasonable samplingduration of the pressure measurement and processing method are proposed to providerelatively more stable (consistent) description of radiation noise spectrum and source levelassessment; the distribution characteristics of the near and far field radiation noise in differentwater depth and submerging depth are briefly exhibited; a method is proposed anddemonstrated to obtain an adjustment diagram for converting the resultant radiation noiselevel within a frequency range of a ship from one environment of water depth and submergingdepth to another based on the calculation results of the same ship in different water depth andsubmerging depth. Finally, the applications of the sono-elastic response analysis method andprogram developed in this thesis are briefly exhibited in two examples of machinery excitedvibrations and sound radiations of full scale ships. The comparisons of the predictions and themeasured results again confirm to some extent the applicability of the major achievementssummarized above.更多还原